1. Field of the Invention
This invention relates to a thermal test method for nondestructive inspection of the quality of welds formed by spot welding, particularly of the diameters of the individual nuggets.
2. Description of the Prior Art
The strength of a weld joint formed by spot welding is measured by making a tension test on the welded members with a tension tester for materials. However, the strength of a spot-welded joint can fairly accurately be estimated by examining the size and fusion condition of the nugget in each weld zone. For visual inspection of the size and appearance of the nuggets, welded members are split with an wedge-shaped implement such as a chisel. Alternatively, the welded members are cut in two across each nugget. These destructive test methods are naturally of use only in sampling inspection.
Practically the one and only method for the nondestructive inspection, which may be either sampling inspection 100% inspection, of spot-welded joints is ultrasonic testing. It is difficult, however, to accurately estimate the size of each nugget by ultrasonic testing. The presence of the impressions of the electrode tips for spot welding on the surfces of the welded members obstructs a smooth scanning of a ultrasonic impulse over the weld whether the testing is conducted by the immersion method or by the contact method. In the case of the contact testing method, the acuracy of the inspection is influenced by the shape and size of the tracer of the testing instrument, too.